Protected magnetic core element



Oct. 23, 1962 D. sHANsKY ETAL PROTECTED MAGNETIC CORE ELEMENT Filed May l, 1958 w 0mm H TSL N 3%@ WHV T Ism/4T mm A ut w.

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tates A general object of the present invention is to provide a new and useful magnetic core apparatus. More specifically, the present invention is concerned with a new and improved magnetic core apparatus which is characterized by its ruggedness and ability to withstand handling as the apparatus is being prepared for use in the manufacturing r assembly of electrical apparatus.

Magnetic core devices are widely used in various types of electrical circuits. One particular type of core widely used in digital data processing circuits is a core hav-ing a rectangular hysteresis characteristic. Magnetic materials useful in making these cores take many ditferent forms. One preferred form of core is a metallic core formed of a relatively thin metallic tape which is wound to form a hollow cylindrical configuration, Sometimes referred to as a toroid. These toroidal tape wound cores, when formed, must be annealed at relatively high temperatures and when so annealed, the resultant core exhibits the desired rectangular hysteresis characteristic essential to certain types of electrical circuits.

It has been found that the manufacture and assembly of tape wound cores heretofore available has been accompanied by a very high rejection rate of the end product. The rejection which renders a core of no value does not necessarily involve the physical breaking of the core material but may involve the mere stressing of the core material in the course of it being handled while being assembled. Mechanical stresses which have been placed on the metal tape cores when they have been heat treated tends to destroy the electrical characteristics of the annealed material so that they are not usable and not matched to other cores of like type and dimens-ion.

It has been the practice to wind these metallic tape cores on ceramic bobbins prior to annealing. Ceramic was selected for the reason that it was capable of withstanding the annealing temperatures which might well go as high as 1000 centigrade. However, the placing of a winding on the core may result in the winding itself causing a stress upon the core material. For this reason, attempts have been made to place protective coverings over the material once it has been annealed. Plastic tapes have been tried but have not been generally successful for the reason that even these protective tapes tend to place a stress upon the core material and when so stressed the core material changes its electrical characteristics.

Ceramic bobbins are subject to other shortcomings in that they tend to score the wires normally wound on the cores as they are threaded through the core due to the abrasive nature of the ceramic. Further, the ceramic is inherently more brittle than other types of materials and physical destruction of the bobbin and thereby the core is much more likely than in the case of a more .rugged material.

The present invention overcomes the basic diiiculty involving the use of magnetic tape cores and ceramic bobbins for the reason that it provides a sturdy and absolute protective covering which is capable of being annealed at the high temperatures required for annealing the core and still have sufficient strength to permit the winding of the core at a subsequent time in the course of a manufacturing operation. The core protective member may be, though not necessarily, metallic so long as it is nonmafg- 3,650,353 Patented Oct. 23, 1962 netic. Metal is preferable for the reason that it can be readily machined and otherwise manipulated for shaping purposes to provide the desired mounting and protection for the core.

It is accordingly a further more specific object of the present invention to provide a new and improved protective covering for a tape wound magnetic core.

A protective material which has been found to be very suitable for use in this configuration is a stainless steel which is nonmagnetic. Stainless steel has the advantage of being able to withstand the high annealing temperatures required in the preparation of the tape cores.

A still further more specific object of the invention is then to provide a new and improved protective covering for a tape wound magnetic core which is formed of stainless steel.

The foregoing objects and features of novelty which characterize the invention as well as other objects of the invention are pointed out with particularity in the claims annexed to and forming a part of the present specification. For a better understanding of the invention, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIGURE 1 is a sectional view of a bobbin member useful in one embodiment of the invention with a metal tape core formed thereon;

FIGURE 2 is a diagrammatic representation of an outer protective member useful in one embodiment of the present invention;

FIGURE 3 is a cross sectional representation of the units of FIGURES l and 2 assembled;

FIGURE 4 is another embodiment of the present invention involving a single supporting and protecting member; and

FIGURE 5 shows the completed form of the unit illustrated in FIGURE 4.

Referring first to FIGURE l, there is here illustrated a bobbin member 10 having a hollow cylindrical section 12 and a circular end wall section 14. Wound on the core portion of the bobbin 12 adjacent the end wall 14 is a metallic tape 16.

Adapted to tit over and protectively cover the tape 16 is a hollow cylindrical cup shaped member or cap 18, as illustrated in FIGURE 2. The cup shaped member 18 has a hollow shank 20 which is adapted to t inside of the section 12 of the bobbin 10. When the protective cup shaped member 18 has been placed over the bobbin 10, the ends of the shank 20 are rolled or otherwise expanded to engage the outer end of the wall portion 14 so that the assembled unit will appear as illustrated in FIG- URE 3. The ends of the shank 2t), when rolled over, will cause the bobbin 10 and the cup shaped member 13 to appear as a solid unitary piece.

As illustrated in the drawings, the length of the side of the cup shaped member 18 does not completely cover the end wall or engage the end wall portion 14 of the bobbin 10. The opening 22 between the end wall 14 and the protective member 18 is necessary to prevent the assembled covering from acting as an electrical short circuit for the core.

In a preferred embodiment of the invention, the bobbin 1) and the cylindrical protecting member 18 were formed of a nonmagnetic stainless steel known commercially as Number 303 l8-8FM stainless steel.

The tape which is wound upon the bobbin is an alloy comprising 4% molybdenum, 79% nickel and 17% iron. The metallic tape formed of this alloy, in one embodiment,

had dimensions of 1A mil. thickness with a width of 1A; inch.

After the tape has been mounted on the bobbin and the protective sleeve -13 has been fastened over the bobbin, the entire assembly is then placed in an annealing oven. In the annealing oven the unit is subjected to a temperature of approximately 1000" centigrade. The use of such a high temperature as this tends to limit the number of materials that can be used for the bobbin in the protective member for the reason that these elements must retain their shape during the annealing process and their electrical characteristics must further not be materially changed. The need for the annealing, however, is to cause the alloy tape to have its characteristics acted upon so as to develop a predetermined electrical characteristic. The characteristic which is desired in the core elements of certain electrical circuits requires a rectangular hysteresis characteristic in the magnetic tape. The presence of this rectangular hysteresis characteristic is useful in circuits for performing logic as well as storing information.

It has been found that if the metal tape which forms the heart of the element is stressed in any way after it has been annealed, its electrical characteristics are subject to change and can well render the end product useless. The presence of a solid sleeve over the solid bobbin member forms an absolute protective cover for the tape. As such, it prevents the tape from being subjected to any stress in the course of a winding operation wherein a number of turns of wire may be wound around and through the assembled units, as illustrated in FIGURE 3.

It is desirable that the inner and outer edges of the assembled unit be rounded suciently to prevent any scoring of the wires threaded through and around the unit. This further enhances the utility of the assembled unit and minimizes the number of units that may be rejected due to shorted windings thereon.

A modiiied form of the apparatus is illustrated in FIG- URES 4 and 5. Here, a single bobbin member 24 is formed with a hollow cylindrical center portion 26 on which a magnetic tape 28 is Wound. yFormed on the bobbin portion 26 are a pair of end walls 30 and 32.

Once the tape 28 has been Wound upon the bobbin portion 26, the outer ends of the wall portions 30 and 32 can be rolled over to form an enclosure for the tape 28 in the manner illustrated in FIGURE 5. As with the assembly illustrated in FIGURE 3, an opening is maintained between the ends of the wall members 30 and 32 as they are rolled over in order to prevent the protective cover from acting as. a short circuit for the unit when assembled.

The materials selected for use in the embodiment shown in FIGURES 4 and 5 may be the same as those of FIG- URE 3. For example, stainless steel of a nonmagnetic type, which is capable of withstanding the high annealing temperatures required for the magnetic tape, may be 4 used to form the protective covering and the support for the magnetic tape.

While, in accordance with the provisions of the statutes, there have been illustrated and described the best forms of the invention known, it will be apparent to those skilled in the art that changes may be made in the apparatus described without departing from the spirit of the invention as set forth in the appended claims and that in some cases, certain features of the invention may be used to advantage without the corresponding use of other features,

Having now described the invention, what is claimed as new and novel and which it is desired to secure by Letters Patent is:

1. An annealable magnetic core assembly comprising a non-magnetic bobbin, a metallic tape of magnetic material Wound on said bobbin to form a toroidal magnetic core, said bobbin including a pair of integral end walls each having a first portion substantially perpendicular to the bobbin axis, each of said walls including a second portion substantially parallel to said bobbin axis and protectively enclosing substantially one-half of the peripheral surface of said toroidal core, said second wall portions including a pair of spaced facing edges extending about the periphery of said core, said bobbin being formed throughout of stainless steel which retains its form at a temperature sufficient to anneal said magnetic tape core.

2. An annealable magnetic core assembly comprising a non-magnetic bobbin, a metallic tape of magnetic material wound on said bobbin to form a toroidal core, said bobbin including an integral flange substantially perpendicular to the bobbin axis and protectively covering an external surface portion of said toroidal core, a non-magnetic hollow, cylindrical cup-shaped member mounted on said bobbin and protectively covering the remaining external surface portions of said core, the edge of said mounted cup-shaped member being spaced from said bobbin ange, said cup-shaped member further including integral locking means axially extending inside said bobbin and engaging said flange, said bobbin and said cup-shaped member being formed throughout of stainless steel which retains its form at a temperature sufficient to anneal said magnetic tape core.

References Cited in the le of this patent UNITED STATES PATENTS 2,469,808 Aske May 10, 1949 2,592,721 Mott Apr. 15, 1952 2,703,392 Rex Mar. l1, `1955 2,768,337 Miller Oct. 23, 1956 2,999,215 Lufcy et al. Sept. 5, 19611 OTHER REFERENCES Performance-Guaranteed Tape Wound Cores, Catalog TWC-A; Magnetics Inc., March 1955. 

